5,093 research outputs found
Kinetic modelling of epitaxial film growth with up- and downward step barriers
The formation of three-dimensional structures during the epitaxial growth of
films is associated to the reflection of diffusing particles in descending
terraces due to the presence of the so-called Ehrlich-Schwoebel (ES) barrier.
We generalize this concept in a solid-on-solid growth model, in which a barrier
dependent on the particle coordination (number of lateral bonds) exists
whenever the particle performs an interlayer diffusion. The rules do not
distinguish explicitly if the particle is executing a descending or an
ascending interlayer diffusion. We show that the usual model, with a step
barrier in descending steps, produces spurious, columnar, and highly unstable
morphologies if the growth temperature is varied in a usual range of mound
formation experiments. Our model generates well-behaved mounded morphologies
for the same ES barriers that produce anomalous morphologies in the standard
model. Moreover, mounds are also obtained when the step barrier has an equal
value for all particles independently if they are free or bonded. Kinetic
roughening is observed at long times, when the surface roughness w and the
characteristic length scale as and where
and , independently of the growth
temperature.Comment: 15 pages, 7 figure
Aspects of CPT-even Lorentz-symmetry violating physics in a supersymmetric scenario
Background fermion condensates in a landscape dominated by global SUSY are
reassessed in connection with a scenario where Lorentz symmetry is violated in
the bosonic sector (actually, the photon sector) by a -even -term. An
effective photonic action is discussed that originates from the supersymmetric
background fermion condensates. Also, the photino mass emerges in terms of a
particular condensate contrary to what happens in the -violation.
Finally, the interparticle potential induced by the effective photonic action
is investigated and a confining profile is identified.Comment: 14 pages. arXiv admin note: text overlap with arXiv:1102.3777 by
other author
Interacting Particles and Strings in Path and Surface Representations
Non-relativistic charged particles and strings coupled with abelian gauge
fields are quantized in a geometric representation that generalizes the Loop
Representation. We consider three models: the string in self-interaction
through a Kalb-Ramond field in four dimensions, the topological interaction of
two particles due to a BF term in 2+1 dimensions, and the string-particle
interaction mediated by a BF term in 3+1 dimensions. In the first case one
finds that a consistent "surface-representation" can be built provided that the
coupling constant is quantized. The geometrical setting that arises corresponds
to a generalized version of the Faraday's lines picture: quantum states are
labeled by the shape of the string, from which emanate "Faraday`s surfaces". In
the other models, the topological interaction can also be described by
geometrical means. It is shown that the open-path (or open-surface) dependence
carried by the wave functional in these models can be eliminated through an
unitary transformation, except by a remaining dependence on the boundary of the
path (or surface). These feature is closely related to the presence of
anomalous statistics in the 2+1 model, and to a generalized "anyonic behavior"
of the string in the other case.Comment: RevTeX 4, 28 page
Formation of Nanopillar Arrays in Ultrathin Viscous Films: The Critical Role of Thermocapillary Stresses
Experiments by several groups during the past decade have shown that a molten
polymer nanofilm subject to a large transverse thermal gradient undergoes
spontaneous formation of periodic nanopillar arrays. The prevailing explanation
is that coherent reflections of acoustic phonons within the film cause a
periodic modulation of the radiation pressure which enhances pillar growth. By
exploring a deformational instability of particular relevance to nanofilms, we
demonstrate that thermocapillary forces play a crucial role in the formation
process. Analytic and numerical predictions show good agreement with the pillar
spacings obtained in experiment. Simulations of the interface equation further
determine the rate of pillar growth of importance to technological
applications.Comment: 5 pages, 4 figure
Desorption Dynamics of Heavy Alkali Metal Atoms (Rb, Cs) off the Surface of Helium Nanodroplets
We present a combined ion imaging and density functional theory study of the
dynamics of the desorption process of rubidium and cesium atoms off the surface
of helium nanodroplets upon excitation of the perturbed and states,
respectively. Both experimental and theoretical results are well represented by
the pseudodiatomic model for effective masses of the helium droplet in the
desorption reaction of m_eff/m_He~10 (Rb) and 13 (Cs). Deviations from this
model are found for Rb excited to the 6p state. Photoelectron spectra indicate
that the dopant-droplet interaction induces relaxation into low-lying
electronic states of the desorbed atoms in the course of the ejection process.Comment: in press, J. Phys. Chem. A (2014
Bacterial Meningitis in Newborn Babies
Objectivo â Conhecer a epidemiologia da meningite bacteriana em recĂ©m-nascidos admitidos na Unidade de Cuidados
Intensivos Neonatais do Hospital de Dona EstefĂąnia.
Doentes e mĂ©todos â Foi feita a revisĂŁo dos processos de recĂ©m-nascidos admitidos na Unidade de Cuidados Intensivos
Neonatais do Hospital de Dona EstefĂąnia de Janeiro de 1985 a Dezembro de 1996 â 12 anos, provenientes da maternidade do
Hospital ou do exterior. Foram excluĂdas as infecçÔes congĂ©nitas e as crianças com idade superior a 28 dias. Definiu-se como
precoce a infecção com inĂcio nas primeiras 72 horas de vida.
Resultados â Houve 36 casos de meningite bacteriana correspondendo a 1,1% das admissĂ”es. A incidĂȘncia de meningite
bacteriana precoce na Maternidade do Hospital foi 0,13 por mil nados-vivos. Vinte e quatro crianças eram do sexo masculino (66,7%), 7 eram pré-termo, 4 de baixo peso e 1 de muito baixo peso. Dez recém-nascidos tiveram meningite precoce (27,8%) e 26 (72,2%) meningite tardia. Houve isolamento do agente bacteriano
no lĂquido cefalorraquidiano em 27 crianças (77,1%): E. coli (n=7); Streptococcus do grupo B(SGB) (n=6); Klebsiella pneumoniae (n=3); Proteus mirabilis (n=2), Listeria monocytogenes
(n=1), Streptococcus bovis (n=1), Staphylococcus aureus (n=1), Neisseria meningitidis (n=2) e Salmonella tiphy (n=1). Houve ainda o isolamento de 3 Gram negativos nĂŁo identificados. A hemocultura foi positiva em 19 de 32 colheitas (59,4%). Na ausĂȘncia de terapĂȘutica antibiĂłtica, em 6 casos a cultura do
lĂquor foi positiva e a hemocultura negativa e noutros 2 ambas as culturas foram negativas. Durante o internamento faleceram 9 recĂ©m-nascidos â mortalidade de 25% e em 11 foram detectadas sequelas.
ConclusĂŁo â Houve um predomĂnio de casos de meningite tardia, em recĂ©m-nascidos de termo e do sexo masculino. Os agentes mais frequentemente encontrados foram a E. coli e a Streptococcus do grupo B
Repercussão das Colheitas de Sangue sobre os Valores de Hemoglobina em Recém-Nascidos de Muito Baixo Peso (RNMBP) Submetidos a Terapia Intensiva
A perda iatrogĂ©nica de sangue constitui um problema comum nas unidades de cuidados intensivos neonatais. O objectivo deste trabalho foi quantificaras espoliaçÔes de sangue para estudos analĂticos em 22 RNMBP durante as primeiras trĂȘs semanas de hospitalização. O nĂșmero mĂ©dio de colheitas por criança e por dia foi IA e o nĂșmero mĂ©dio de colheitas por criança no perĂodo estudado foi 29.7. O valor cumulativo mĂ©dio de sangue espoliado pelo 21." dia foi 18,7 ml/kg. Os valores mĂ©dios de hemoglobina nas primeiras 12 horas de tida e no 21." dia foram respectivamente 16.4 e 12.9 gr/d1. Verificou-se
uma relação estreita entre o volume de sangue extraĂdo e o volume de sangue transfundido. sugerindo este facto que. em geral. as transfusĂ”es sĂŁo efectuadas
por necessidade de compensar as perdas sanguĂneas relacionadas com as colheitas de sangue.
Conclui-se que as espoliaçÔes repetidas de sangue para anålises laboratoriais se repercutem significativamente nos valores de hemoglobina dos recém-nascidos
pretermo e de MBP sendo portanto desejĂĄvel que tais espoliaçÔes sejam rigorosamente quantificadas e reduzidas ao mĂnimo tendo em conta os riscos das transfusĂ”es de sangue
Application of the penalty coupling method for the analysis of blood vessels
Due to the significant health and economic impact of blood vessel diseases on modern society, its analysis is becoming of increasing importance for the medical sciences. The complexity of the vascular system, its dynamics and material characteristics all make it an ideal candidate for analysis through fluid structure interaction (FSI) simulations. FSI is a relatively new approach in numerical analysis and enables the multi-physical analysis of problems, yielding a higher accuracy of results than could be possible when using a single physics code to analyse the same category of problems. This paper introduces the concepts behind the Arbitrary Lagrangian Eulerian (ALE) formulation using the penalty coupling method. It moves on to present a validation case and compares it to available simulation results from the literature using a different FSI method. Results were found to correspond well to the comparison case as well as basic theory
Maxwell Chern Simons Theory in a Geometric Representation
We quantize the Maxwell Chern Simons theory in a geometric representation
that generalizes the Abelian Loop Representation of Maxwell theory. We find
that in the physical sector, the model can be seen as the theory of a massles
scalar field with a topological interaction that enforces the wave functional
to be multivalued. This feature allows to relate the Maxwell Chern Simons
theory with the quantum mechanics of particles interacting through a Chern
Simons fieldComment: 12 pages, LaTe
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